Edit: SOLVED. See post #22 for video of fan problem and post #26 for fix

'08 Z51 mn6, P1 Procharger, low boost, stock everything else.

Recently had my radiator fan connector melt, so I re-wired and replaced it with a heavy duty, high amperage connector. I also purchased a used Dewitts radiator from a forum member (not the shorty version) with the built-in TOC and EOC. Connector and radiator install went flawlessly, no leaks, no issues. Burped the coolant system 3x before the reservoir stayed full and car maintained temps at idle.

Prior to installing Dewitts, during 90*+ ambient temp days, I was seeing temps:
Coolant: 205-210 cruising/idling, 210-220 traffic, 215-225 spirited canyon driving
Oil: 205-215 cruising, same in traffic, 225-245 spirited driving

After installing Dewitts, during 75-80* ambient temp I am seeing:
Coolant: 200-205 idle, 205-210 cruising, 205-210 traffic, 212-220 after only a couple half-3/4 throttle pulls.
Oil: 210-215 cruising, same in traffic, 225+ spirited driving.

My fan is also acting relatively erratic. It does not stay on high when the car is hot, but rather goes on high speed for 1sec, then low speed for 1sec, high, low, high, low, repeat, repeat, repeat. It does this with the AC on or off.

Radiator, condenser, and intercooler are all cleaned out (no blockage). From everything I've read, members claim 180-200* coolant temps when cruising and rarely/never getting over 210. Are these coolant temps normal?

 

So hard to compare with so many variables. I did a Dewitt’s in my A&A car about two months ago. EOC/TOC version and my numbers are pretty similar to yours in 75* -90* temps. My car likes to settle in to coolant temp of 207* quickly and stays there when driving at steady speeds from 50-80mph. Seems like most times and outdoor temp the coolant is 207*. Oil about 212 or so at the same time. Goes up when doing quick hard pulls but to tell the truth I’ve been leaving my trans temp numbers on the display because I recently had it rebuilt. I think your numbers are ok but no expert here.

 

Make sure coolant is proper mixture but radiator by itself does very little. On highway should have a bit more cooling and capacity if it is setup properly but for low speed it may even cool worse than stock as stock fan has to draw air through a thicker core which hurts performance.

 

I like using home cooling to explain things because everyone seems agree and understand. So, I have a 2 ton AC system on my house and I set the temperature to 70 degrees. Then I upgraded the system to a 5 ton unit and set the temperature to 70 degrees I will see absolutely no change. I have more capacity, I'm just not asking for it. Maybe I could cool the house down to 50 degree now, but I am not asking for that.
Okay, now your car. You added a higher capacity radiator and if you want to get it to run cooler you need to tell it to. Install a lower setting, high flow aftermarket thermostat and reprogramming the fans to come on earlier will do the trick.

 

Indeed I have noticed that it cools back down much quicker (e.g. after a pull it will be around 216 but will cool back down to 207 faster than previously.

Mixture is 50/50 distilled water and fresh dex-cool. Didn't think of it that way. I guess a Prospeed setup would be my next step?

Thanks for the analogy, that makes sense. I do have a 160* stat but the fans have not been programmed to come on sooner. On my next tune I suppose I should have them look into the fans?


I'm still not sure why the fans are running erratically. Fast/slow/fast/slow repeatedly. They won't stay on high (or a consistent speed), regardless of coolant/oil temps.

 

Maybe a loose connection at the splice or the new connector is defective?

 

I suspect my fan speed is also oscillating. I have the ProSpeed, with a full size DeWitt's. I believe this because my voltage indicates this by it's cycling. It cycles about 1.0-1.5 volts at idle maybe every second when hot (above 205*F ECT's). I haven't checked the actual fan speeds though. That's with stock alternator, AND with a new Mechman 170amp.
I had my car tuned at a great shop and assumed this was just the programs characteristics.

FWIW; my car cools down nicely when cruising at 60< mph. But I can tell the ProSpeed must have more restrictive air flow than the stock fan system while cruising (not relying on the fans), as it doesn't cool down as quickly when I speed up to hiway speeds...

 

82* outside at night and the car is hovering at 216-219* idling with the AC off in the drive thru. With the AC on, it climbed to 226* before the AC cut out. Something isn’t right.

 

Yeah somethings not right. Water pump maybe?

 

I went back to the top post and I noticed you purchased the radiator used. Maybe the seller was trying to get rid of a problem. Sometimes a pressure spike in the system can expand the flat cooling tubes and this crushes the fin and closes off the air path through the radiator. It crushes the fin very evenly so it's hard to tell unless you are really looking for it. An easy test is to slide a zip tie through the core and it should come out the other side. If you can't do it, something is wrong. See these two images for a good and bad core



BAD



GOOD

 

Interesting.
Bought one of your rads a couple months ago and just curious. What temp # would cause such an issue with a Dewitt’s ?
Can the Same happen with a stock C6 rad? I overheated my stocker and wondering if that could have happened to it!

 

Temperature will not do it. This is typically caused by engine exhaust, compression stroke, or backfire getting into the cooling system via a bad head gasket or compression leak.

 

That's some good information, Thanks Tom.

DJ

 

Hi,

I would check your fan setting. Make sure they are not programmed for anything more than 89%.

I was dealing with cooling issues three or four years ago and found that if I programmed the fans for anything over 90% the stock fan module defaults to like 10 or 20%. I was able to do it just using HP tuners manual mode just sitting in the garage. Its been a while but might be worth looking into. My car is down at the moment or I would double check again for you. If you have HP Tuners you could give it a try.

Again its been a while and I can't 100% guarantee anything but it sure would be good information to know.

DJ

 

So I took about a 6 hour round trip last weekend. At speed, the car hovered around 198-207*, which is fine. If I rowed through a few gears at WOT it'd immediately climb to about 217*, but quickly settle back around 200* in about a minute. (This is 70-85* ambient temps.) Car idled around 214*. (Fans cycling high/low. )If it were 90*+ outside, I'd be overheating at idle.
I think my issue is that my fan never stays on high. It cycles high/low/high/low.

Additional tests:
-I pulled the coolant temp sensor at idle (which should command the fans to go full speed as the ECM can't detect any coolant temp) and the fans still cycle high/low, over and over again.
-I suspected the signal wire between the ECM and the PWM had a bad connection (as I replaced the old fan connecter with a commercial grade, high amperage connector). So I pulled the signal wire out of the new connector , and wired it directly, outside of the connector. Tested again, still cycles high/low.
-Fan fuse is good
-Checked the fan ground on the passenger front inner fender well in the engine bay - it's good.


I'm not sure why the fan won't stay on high.
Prior to my connector melting, the fan functioned properly. THE ONLY CHANGES I MADE: I disconnected the battery, installed a Dewitt's, and replaced the connector. Properly crimped all connections (hydraulic crimper) and they're all solid. Could it be my ECM or my PWM/fan modulator?

I got under the car and slid a zip tie through the radiator in about 10 different places. Never an issue sliding it through.

 

Just to be clear--is the ECM still controlling the fan or does it have it's own sensor now?

If so, I would look into what the ECM is seeing and commanding first. I'd want to know what coolant temp the ECM is seeing, and more importantly, what coolant temp the fans are SUPPOSED to be coming on and ramping up (factory fans are not a low/high setup, they go from 0 to 100%). i.e. is the fan doing what it's told to do or not?

I've seen in the past where the fans were basically being turned up and down like that just because of the AC system and not even because of water temp. That usually causes them to cycle like you are seeing and not stay on as high as you'd like.

What's the tune look like in terms of fan settings?

The stock settings are pretty slow to ramp up. A lot of times AC system pressure will kick them up before coolant temp does. I doubt it is a wiring issue personally. It sounds like you have done a good job with the wiring already.

 

Wow!! What great information in this thread!!
Tom, great customer support!! Very rare to see in the world today!! Especially on your product that was purchased used, and not from you! That is the kind of company I want to do business with!!! Great job Tom!!! Thumbs up!!!
Andy at A&A started restoring my faith in caring business owners again, and Tom just solidified it for me!! There still are people out there who care about the people who purchase their products... and will step in to help when an issue arises!!!
Thank you for that Tom!

 

Here are the factory fan settings FYI

 

As you can see, unless you are tuned, 214F the fan is only on at 1/2 speed and barely getting started. So it isn't anywhere near on "high" yet. What theandrewo posted is exactly like how a stock corvette should work, as design by GM. Not sure where he gets if it was hotter it would be overheating, as car is working as designed.

 

I'm not sure what the fan settings are. The car had a blower installed and was tuned prior to me purchasing it. I guess my next step is to get a scanner hooked up to see what the ECM is commanding the fan to do?

The thing is, the fan won't stay constant at any speed. Not 20%, not 50%, etc. As soon as it's commanded to come on via AC pressure or coolant temp, it ONLY cycles high/low repeatedly. It did not do this prior to changing the fan connector. Even with coolant temp sensor disconnected (and it should be 90%), it still cycles.

Sometimes it won't come on at all. I was idling in the drive-thru 2 weeks ago (no AC), 75* ambient temps, and the fan would not come on. Coolant ran up to 250* until I finally got out of the drive-thru and got some airflow. The car has a blower. I installed a 160* stat but it has not been tuned for it yet.